Treatment of wax



Aug.' 17, 1937. G. W. RlTTER 2,089,984

TREATMENT OF WAX Filed Jan. 50, 1935 :inventor /ZS Cttorneg Patented Aug. 17, 1937 UNlTED STATES acatar PATENT OFFICE TREATMENT OF WAX Application January 30, 1935, Serial No. 4,161

12 Claims.

The present invention relates to improvements in a process for the separation of hydrocarbon oil-wax mixtures into components and more particularly to improvements in the process dis- 5 closed in co-pending application of S. W. Ferris,

Serial No. 4,157, filed January 30, 1935.

Briefly, the process disclosed in the co-pending application of Ferris consists in preparing an oil-wax mixture, for example, as by distillation,

l which upon cooling to the desired separating temperature will crystallize wax to the extent of substantially 10% or less of the total volume of the mixture; or the dilution of a wax-bearing stock with a suitable solvent, so that upon cooling to l the desired separating temperature, wax will crystallize to the extent of 10% or less of the total volume of the mixture. The oil-wax mixture so prepared is then cooled to the desired temperature, with or without agitation, in such a manner as to effect a dispersion of the wax crystals throughout the mother liquor with reasonable uniformity. If agitation is resorted to, the cooled mother liquor containing the wax crystals is thereafter permitted to stand, unagitated, for sufficient time to effect the formation of a highly porous wax mass, the structure of which has appreciable mechanical strength, such mass containing less than substantially of solid wax per unit volume of the mass. of the mother liquor from the cooled wax mass is then accomplished by passing a displacing liquid, preferably an oil solvent, through the mass in such a manner that a substantially horizontal interface is maintained between the mother liquor in the mass and the displacing liquid, the displacement pressure (differential pressure or pressure drop through the wax mass) being of the order of 5 lbs/sq. in., or less per foot depth of wax mass, and the concentration of crystalline wax .o being less than substantially by volume of the mass in which mother liquor is still present. The displacement step is usually accompanied by the settling or compacting of the wax mass from which the mother liquor is being removed, but such compacting is controlled to prevent the concentration of crystalline wax in the mass from exceeding substantially 20% by volume of the mass. This control is obtained by the proper adjustment of the quantity of wax crystallized from the mother liquor to form the initial wax mass, the rate and degree of cooling, the differential pressure required for displacement and the gravity differentials between wax, mother liquor and displacing liquid. Upon completion of the 55 displacement operation the solvents employed The displacement may be separated from the oil and wax fractions by distillation.

In carrying out the process, it is necessary to control the quantity of Wax in the mother liquor so that the crystalline wax content of the mass f.

resulting from the chilling of the mother liquor Will not exceed substantially 10% of any unit Volume of the mass at the beginning of the displacement operation. In most instances, it has been found that the crstalline wax contained in the wax mass at the beginning of the displace'- ment step should be of the order of from 1% to 6% by volume, and preferably of the order of from 2.5% to 4.5% by Volume; it may, however, be as high as 10% by volume depending upon the character of the wax crystals. Furthermore, in general, the differential pressure required in effecting displacement does not exceed substantially 5 lbs/sq. in. per unit (l foot) depth of the wax mass, and usually at the outset does not exceed 2 lbs/sq. in. It is to be understood, however, that at some stage of the operation, and particularly during the latter part thereof, the pressure may be somewhat in excess of 5 lbs/sq. in. per l foot depth of the mass.

In the displacement-process as above outlined, it has been customary to introduce the displacing or Washing liquid into the displacement vessel after the desired quantity of wax crystallized from the mother liquor to form the porous wax mass, the step of displacing the mother liquor from the mass being effected immediately after such introduction of displacing liquid. In some instances it has been found that during the cooling step and/or during the initial stage of displacement proper, cracks or channels will develop within the mass and portions of the mass Will not be washed free of mother liquor, due to the by-passing of displacing or washing liquid thru the channels so formed.

In contrast to this method of operation, I have found that more uniform results may be obtained by maintaining a body of displacing or washing liquid in contact with the surface of the mother liquor in the displacement vessel during and/or after the cooling thereof to effect crystallization of wax to form a porous wax mass. The body of displacing liquid maintained in contact with the mother liquor and/or the wax mass, but without substantial admixture therewith, serves to prevent Vaporization of solvent from the mother liquor and drying of the surface of the wax mass, thus inhibiting the formation of cracks or channels in the wax mass. Furthermore, by maintaining the displacing liq- Cil uid in contact with the surface of the mass for a peri-od, for example, of the order of from about 1 to about 8 hours, an appreciable movement of the wax mass into the displacing liquid is 5 effected, the magnitude of such movement depending upon the specic gravity differentials between the displacing liquid, the mother liquor and the wax. Prior to the displacement step. proper, and during the period in which the displ-acing liquid is maintained in contact with the surface of the wax mass, the mother liquor in that portion of the mass which has penetrated or entered the displacing liquid is replaced by said liquid without substantial disruption of the llinterface between the mother liquor and such liquid. Thus a partial washing of the wax mass is accomplished before the step of actual displacement is undertaken.

For a clearer 'understanding of my invention, reference is made to the accompanying drawing which shows an apparatus suitable for carrying on my process.

From a steam jacketed stock tank I, 40 parts, for example, of a wax-bearing distillate from East Texas crude oil having a-pour test of 125 F. and a Saybolt Universal viscosity of 60 seconds at 210'J F., is Withdrawn through valvecontrolled'pipe 2 and pumped by pump 3 through Valve-controlled pipe 4 into mixing tank 5 provided with heating coil 6 and stirrer 1. Simultaneously or subsequently 60 parts, for example, of ethylene dichloride is withdrawn from solvent tank 8 by mea-ns of valve-controlled pipe 9 and pumped by pump I8 through valve-controlled Ypipe 4 into mixing tank 5. Herein the solvent and distillate containing wax is agitated at a temperature of, for example, 120 F. until a homogeneous solution is obtained. The resulting solution is passed from the mixing tank 5 by means of valve-controlled pipe I I and is pumped by pump I2 through valve-controlled pipe I3 to chilling device I, wherein the solution is cooled until4 the temperature is of the order of, for example, 85 F. and a portion of the wax has crystallized. This oil-wax-'solvent mixture is passed from the chiller I4 by means of valvecontrolled pipe I5 into the brine-.jacketed displacement tower I6 above the screen I1. Prior to the introduction of the chilled mixture into the tower I6, air pressure is applied to brine tank I8 through valve-controlled pipe I9 provided with valved vent 19a and brine is forced through valve-controlled p-ipe 28 and pipe 2l into the conical lower section of tower I5 until it barely e5 covers the scr-een I1. rIlhe brine and screen I1 thus support the chilled oil-wax-solvent mixture in the tower I6. Thereafter, a quantity of displacing liquid, for example 40 parts of naphtha of 88 A. P. I. gravity, is passed from the displacement liquid tank 22 through valve-controlled pipe 23, cooled to about 85 F. in cooling .coil v24 and introduced into the displacement tower I6 by means of valve-controlled pipe 25, above the surface of the chilled oil-wax-solvent mixture contained therein. The displacing liquid is introduced in such a manner as to prevent substantial disturbance of or admixture with the wax mass from which the oil and solvent are to be displaced. The displacing liquid and the oil-wax-solvent mixture contained in the displacement tower I6 is then cooled at the rate of, for example, 1 F. to 4 F. per hour until the temperature is of the order of, for example, 65 F. and the desired nal quantity of wax has crystallized out. The cooling in the tower I6 may be effected by circulation of cold brine in the tower jacket and/or by the'employment of brine coils or pipes (not shown) installed within the tower. The contents `of the tower I6 are preferably allowed to remai-n in a quiescent state during the iinal cooling period, in which time the wax crystals form an agglomerate mass of appreciable mechanical strength while still retaining a high degree of free space or porosity thruout which the mother liquor is distributed. During the final cooling period, the wax mass tends to settle upwardly to some extent, due to the fact that the specific gravity of the vwax is less than that of the oil and solvent, and the upper portion of the mass penetrates or enters the layer of displacing liquid, i. e., the naphtha. The oil and solvent initially contained in that portion of the mass is replaced by the naphtha and that portion of the mass is thus freed of oil and solvent to a substantial extent during the nal cooling period.

At the completion ofthe nal cooling period brine is withdrawn from the bottom of tower i6 and returned to the brine tank I8 by means of valve-controlled pipe 20. Oil and solvent from the wax mass, displaced downwardly by the displacing liquid, is withdrawn from the bottom of tower I6 and passed through Valve-controlled pipes'26 'and 21 into receiving or heavy eiilux tank 28. If necessary, slight pressure may be applied to the tower I6, above the level of its contents, by means oi valve-controlled air line 29 provided with valved Vent 3D. The differential or displacement pressure is preferably maintained at less than 5 lbs/sq. in. per 1 foot depth of the wax mass, in order to prevent undue compacting of the wax crystals. When substantially all of the oil and solvent (heavy efflux) has been displaced from the wax mass into receiving tank 28, as evidenced by a marke-d change in gravityl or other critical property of the liqiLid issuing from the tower I6, the liquid thereafter withdrawn from the tower isdiverted into? receiving or light eiTluX tank 3l by closing valve-controlled pipe 21 and opening valve-controlled pipe 32.

This light efllux will consist primarily Vor" displacing liquid containing residual oil and solvent which has been washed from the wax mass. The

displacing or washing operation is preferably continued until the effluent from tower I6 is principally displacing liquid.

At the completion of the displacing or washing operation, the wax mass containing residual displacing liquid is forced upwardly and out of tower I6 through valve-controlled pipe 33 into wax receiving tank 34, by means of brineV introduced into the bottom of the tower from brine tank I3.v If necessary, the wax mass contained in tower I6 may be rendered more fluid by the ap-V plication of steam inthe jacket surrounding said tower. The heavy efflux (oil and solvent) in tank 28, the light efllux (oil, solvent and displacing liquid) in tank 3|, and thewax containing residual displacing liquid may be withdrawn from their respective receiving tanks by means of Valve-controlled pipes 35, 36 and 31 and passed to distilling apparatus (not shown) wherein the solvent, i. e., ethylene dichloride and the displacing liquid, i. e., naphtha, may be separated and recovered from the oil and wax.

While, in the above instance, I have described the chilling of the solution of oil stock and solvent from the mixing tank 5 as being effected partially within the chiller I4 and partially within the displacement tower I6, I'may, if desired, pass the Cal heated solution directly to the tower by. means of Valve-controlled by-pass 38 and effect such chilling entirely within the tower I6. Y In this case, the displacing liquid may or may not be cooled in the cooling coil 24 prior to the introduction thereof into the displacing tower I6 above the level of the solution contained therein'. y

As an alternative method of operating I may chill the solution entirely in the chiller I4 prior' to the introduction thereof into the displacement tower I6. The latter method may be carried out by passing the heated solution directly from mixing vessel 5 through valve-controlled pipe i3, chiller I4 and valve-controlled pipe I5 into tower I6. A quantity of displacing liquid, preferably cooled entirely in cooling coil 24 is thereafter introduced into the tower I6 above the level of the mixture contained therein. In this instance, the chilled mixture is preferably allowed to remain in -a quiescent state within tower I6 for a period of, for example, 4 hours, during whichl time the crystals form an agglomerate mass having appreciable mechanical strength while still retaining a high degree of free space thruout which the mother liquor is distributed. Due to the gravity differential between the wax and the mother liquor -a certain amount of upward settling of the latter occurs, so that at the end of the quiescent period a lower layer of relatively wax-free oil solution is present which may be about 30% of the volume of the total charge and the upper portion of the wax mass has penetrated into the body of the displacing liquid. This layer is drawn off from the bottom, yat the same time the wax mass settles until upon completion of the removal of the wax-free solution, the bottom of the wax mass rests upon the screen. The displacement step is then carried on as above described.

The process above described is given yas exemplary of the separation of hydrocarbon oil-wax mixtures by downward displ-acement. In downward displacement the specic gravity of the displacing liquid is less than that of the wax-containing mixture and may be greater or less than that of the wax. However, it is to be understood that my process may be equally well applied to the sep-aration of oil-wax mixtures by upward displacement. In the latter instance, the displacing liquid is of greater specific gravity than the wax-containing mixture and is preferably of less specic gravity than the wax. The displacing liquid is introduced at the bottom of the displacement vessel, beneath the mixture contained therein and displacement is effected by introducing brine beneath the layer of displacing liquid and forcing the latter upwardly into and thru the wax mass, the mother liquor from such mass being discharged from the top of the displacement vessel.

In any event, the relationship between the specific gravity of the displacing liquid and the oil (or mother liquor) is so chosen that the systern will reni-ain gravitationally stable, i. e., light displacing liquid above a heavier mother liquor or oil-solvent, or a heavy displacing liquid beneath a lighter mother liquor or oil-solvent. In other words, in such gravitationally stable system t there will be no tendency for the liquids to exchange places or intermingle, since the heavier liquid is always beneath the lighter liquid, regardless of the composition of the liquids.

In the description of my process given hereinabove, I have shown that ethylene dichloride.

may be employed as the crystallizing solvent and naphtha as the displacing liquid. In addition thereto, I may also employ the lconventional dewaxing solvents such as acetone, acetone-benzol, alcohols, esters, ethers, halogenated hydrocarbons and liqueed normally gaseous hydrocarbons.

For brevity, in the appended claims, the terms solvent liquid and displacing liquid are to be understood to comprehend those compounds in which oil is readily miscible and wax is relatively immiscible at the temperatures employed in the separation of the oil and wax. Also, the

term wax mass as employed herein and in thev appended claims comprehends a porous mass or body of Wax crystals containing oil or oil and solvent distributed therethrough.

'What I claim is:

1. A process for separating a hydrocarbon oilwax mixture into fractions respectively richer inl oil and wax constituents thereof, which comprises producing a w-ax-containing mixture, cooling said mixture to eiect crystallization of wax to form a wax mass containing less than substantially 10% by volume of crystalline wax, disposing in contact with said wax mass and without sub-- stantial admixture therewith, a quantity of displacing liquid having a specific gravity sufciently different from that of the oil and wax constituents to maintain gravitational stability of the liquids and to cause at least a portion of said wax mass to migrate into the displacing liquid, and displacing from said wax mass, without substantial agitation and under a low differential pressure, the liquid constituentsl thereof with said displacing liquid.

2. A process for separating a hydrocarbon oilwax mixture into fractions respectively richer in oil and wax constituents thereof, which comprises producing a wax-containing mixture, cooling said mixture to effect crystallization of wax to form a wax mass containing about 1% to about 6% by volume of crystalline wax, disposing in contact with said wax mass and without substantial admixture therewith, a quantity of displacing liquid having a specific gravity sufliciently different from that of the oil and wax con-` stituents to maintain gravitational stability of the liquids and to cause at least a portion of said wax mass to migrate into the displacing liquid, and displacing from said wax mass, without substantial agitation and under a differential pressure of less than substantially 5 lbs/sq. in. per 1 foot depth of the wax mass, the liquid constituents thereof with said displacingliquid.

3. A process for separating a hydrocarbon oilwax mixture into fractions respectively richer in oil and wax constituents thereof, which comprises producing a wax-containing mixture, cooling said mixture in the presence of a quantity of displacing liquid and without substantial admixture therewith, to effect crystallization of wax to form a wax mass containing less than substantially 10% by volume of crystalline wax, said displacing liquid having a specic gravity sufficiently different from that of the oil and wax constituents to maintain gravitational stability of the liquids and to cause at least a portion of said wax mass to migrate into the displacing liquid, and displacing from said wax mass, without substantial agitation and under a low differential pressure, the liquid constituents thereof with said displacing liquid.

4. A process for separating a hydrocarbon oilwax mixture into vfractions respectively richer in oil and wax constituents thereof, which comprises producing a wax-containing mixture, cooling said mixture in the presence of a quantity of displacing liquid and without substantialy admixture therewith, to effect crystallization of Wax to form a wax mass containing about 1% to about 6% by volume of crystalline wax, said displacingL Y liquid having a specific gravitysufficiently different from that of the oil and wax constituents to maintain gravitational stability of the liquids and to cause at least a portion of said wax mass to migrate into the displacing liquid,Y and displacing from said wax mass, without substantial agitation and under a differential pressure of less than substantially 5 lbs/sq. in. per 1 foot depth of the wax mass, the liquid constituents thereof with said displacing liquid.

5. A process for separating a hydrocarbon oilwax mixture into fractions respectively richer in oil and wax constituents thereof, which comprises producing a wax-containing mixture, partially cooling said mixture to effect crystallization of a portion of the j wax, disposing in `contact with the partially cooled mixture and without substantial admixture therewith, a quantity ofY displacing liquid, further cooling said mixture in the presence of said displacing liquid to form a Wax mass containing less than substantially 10% by volume of crystalline wax, said displacing liquid having a specic gravity sufficiently different from that of the oil and wax constituents to maintain gravitational stability of the liquids and to cause at least a portion of said wax massto migrate into said displacing liquid, and displacing from said wax mass, without substantial agitation and under a low differential pressure, the liquid constituents thereof with said displacing liquid.

6. A process for separating a hydrocarbon oilwax mixture into fractions respectively richerin oil and wax constituents thereof, which comprises producing a wax-containing mix-ture, partially cooling said mixture to effect crystallization of a portion of the wax, disposing in contact with the Vpartially cooled mixture and Without substantial admixture therewith, a quantity of displacing liquid, further cooling said mixture in the presence of said displacing liquid to form a wax mass containing about 1% to about 6% by volume of crystalline wax,l said displacing liquid having a specific gravity sufliciently different from that of the oil and wax constituents to maintain 'gravitational stability ofthe liquids and to cause atleast a portion of said wax mass to migrate into said displacing liquid, and displacing from said wax mass, Without substantial agitation and under a differential pressure of less than substantially 5 lbs/sq. in. per 1 foot depth of the wax mass, the'liquid constituents thereof with said displacing liquid.

7. A process for separating a hydrocarbon oilwax mixture into fractions respectively richer in oil and wax constituents thereof, which cornprises diluting said mixture with a solvent liquid,

i cooling the diluted mixture to effect crystallizationof wax `to form a wax mass containing less than substantially 10% by volume of crystalline wax, disposing in contact with said wax mass and without substantial admixture therewith, a quantity of displacing liquid having av specific gravity sufficiently dilierent from that of the.

oil-solventand wax constituents Vto maintain gravitational stability of the liquids and to cause at least a portion of said wax mass to migrate into the" displacing liquid,'and displacing from said Wax mass, without substantial agitation and under a relatively low differential pressure, the liquid constituents thereof with said displacing liquid.

8. A process for separating a hydrocarbon oilwax mixture into fractions respectively richer inA oil and wax constituents thereof, which comprises diluting said, mixture with a solvent liquid, cooling the diluted mixture in the presence of a quantity of displacing liquid and without substantial admixture therewith, toY effect crystallization of Wax to form a wax mass containing less than substantially 10% by volume of crystalline wax, said displacing liquid having aV specific gravity suiciently different from that of the oil-solvent and wax constituents to maintain gravitational stability of the liquids and to cause at least a portion of said wax mass to migrate into the displacing liquid, and displacing from said Wax mass, without substantial agitation and under a relatively low differential pressure, the liquid constitue-nts thereof with said displacing liquid.

9. A process for separating a hydrocarbon oilwax mixture into fractions respectively richer inY oil and wax constituents thereof, which comprises diluting said mixture with a solvent liquid, partially cooling the dilutedV mixture to effect crystallization of a portion ofthe wax, disposing in contact with the partially cooled diluted mixture and without substantial admixturetherewith, a quantity of displacing liquid, further cooling the diluted mixture in the presence of said dis-placing liquid to form a wax mass containing less than substantially 10% by volume of crystalline wax, said displacing liquid having a specific gravity sufliciently different from that ofthe oil-solvent and wax constituents lto maintain gravitational stability of the liquids and to cause at least a portion of said wax mass to migrate into said displacing liquid, ,and displacing from said wax mass, without substantial agitation and under a relatively low differential pressure, the liquid constituents thereof with said displacing liquid.

10. A processfor separating a hydrocarbon oilwax mixture into fractions respectively richer in oil and wax constituents thereof, 'which comprises adding to said mixture a solvent liquid, heating such adrnixture to a temperature sufcient to effect solution, cooling the solution to effect crystallization of wax to form a wax mass containing less than substantially 10% by volume of crystalline wax, disposing in contact with said wax mass and without substantial adniixture therewith, a quantity of displacing liquid having a specific gravity sufficiently different from that of the oil-solvent and wax constituents to maintain gravitational stability of the liquids and to cause at least a portion of said wax mass to migrate into the displacing liquid, and displacing from said wax mass, without substantial agitation and under a relatively low differential pressure, the liquid constituents thereof with said displacing liquid.

11. A process for separating a hydrocarbon oilwax mixture into fractions respectively ric-her in oil and wax constituents ther-cof, which comprises adding to said mixture a solvent liquid, heating such admixture toI a temperature sufcient to effectsolution, cooling the solution inY the presence of a quantity of displacing liquid and without substantial admixture therewith, to effect crystallization of wax to Vform a wax mass containing less than substantially 10% volumeof crystalline wax, said displacing liquid byv having a specic gravity suiiciently different from that of the oil-solvent and Wax constituents to maintain gravitational stability of the liquids and to cause at least a portion of said Wax mass to migrate into the displacing liquid, and displacing from said Wax mass, Without substantial agitation and under a relatively low differential pressure, the liquid constituents thereof With said displacing liquid.

12. The process for separating a hydrocarbon oil-Wax mixture into fractions respectively richer in oil and Wax constituents thereof, which comprises adding to said mixture a solvent liquid, heating such admixture to a temperature sufiicient to effect solution, partially cooling the solution to effect crystallization of a portion of the Wax, disposing in Contact With the partially cooled solution and Without substantial admixture therewith, a quantity of displacing liquid, further cooling the solution in the presence of said displacing liquid to form a Wax mass containing less than substantially 10% by volume of crystalline wax, said displacing liquid having a speciiic gravity sufliciently different from that of the oil-solvent and Wax constituents to maintain gravitational stability o1" the liquidsv and toI cause at least a portion of said Wax mass to migrate into said displacing liquid, and displacing from said wax mass, Without substantial agitation and under a relatively low differential pressure, the liquid constituents thereof with said displacing liquid.

GEORGE W. RITTER. 

